A flexible, resilient, self-sealing (self-closing), slit-type valve has a slit or slits which define a normally closed orifice that opens to permit flow therethrough in response to an increased pressure differential across the valve (e.g., resulting from an increased pressure on one side of the valve, or from a reduced external ambient pressure compared to the pressure on the other side of the valve.). Such valves are typically designed so that they automatically close to shut off flow therethrough upon a reduction of the pressure differential across the valve.
A flexible, resilient, self-sealing, slit-type valve typically opens when subjected to a predetermined pressure differential across the valve that is sufficiently high for the particular valve design, and the valve closes when the pressure differential across the valve drops to some lower value. In valves of this type, the “opening” pressure differential is typically significantly greater than the valve closing pressure differential.
The inventor of the present invention has discovered that in some applications it can be desirable to minimize the difference between the pressure differential at which the valve opens and the pressure differential at which the valve closes. For example, the inventor has discovered that in certain applications involving the pumping of fluid through a system containing the valve, it would be desirable to have the valve closing pressure differential be only slightly less than the valve opening pressure differential—especially in anti-free flow applications wherein the valve is installed to function as an anti-free flow valve that must be initially opened by upstream pressure produced by the pump. The higher the pressure differential required to open the anti-free flow valve, the more energy it is required to operate the pump to open the valve and deliver the fluid. That greater energy requirement results in greater electric energy and power consumption (which more quickly draws down the charge on a battery if a battery is utilized to provide electric power).
In some applications it is desirable to minimize the energy consumption of the pump. For example, one such application is the use of in a pump-operated feeding set in a hospital environment for providing a nutritional fluid (“enteral formula”) to a patient via tubing connected to the patient. A typical pump-operated feeding set includes (1) a suspended bag or bottle of enteral formula, (2) tubing extending from the bottom of the bag, (3) a pump cassette incorporating a pump acting on the tubing extending from the bottom of the bag so as to a meter (i.e., control) flow through the tubing from the bag at a desired flow rate (which is typically effected by adjusting the pump operation), and (4) tubing extending from the pump cassette to the patient. If a pump cassette were not provided to control flow through the tubing from the bag to the patient, the enteral formula would flow from the elevated bag through the tubing under the influence of the force of gravity and could not be easily controlled to a desired flow rate. A pump cassette interacting with the tubing can restrict the flow of enteral formula to a rate that is less than the free flow rate that would occur under the unrestricted gravity flow condition. The pump cassette can be adjusted to provide flow to the patient at a desired flow rate (typically no greater than the free flow rate that would occur through tubing without a pump cassette engaged). Typically, the pump cassette is adjustable to provide a flow rate that results in feeding the patient over a period of time that may be many minutes or many hours.
The feeding set can include one or more auxiliary clamps to squeeze the tubing closed so as to prevent free flow from the bag when the pump cassette is removed from engagement with the tubing.
It has been discovered that it would be desirable to provide an additional “back-up” way to prevent gravity free flow from the bag into the patient if the pump cassette is deliberately removed from the tubing or if the pump cassette fails or if the pump cassette is accidentally dislodged from engagement with the tubing. It has been discovered that a flexible, resilient, self-sealing, slit-type valve according to the present invention can be effectively employed to prevent such gravity free-flow.
When a self-sealing valve is employed as an anti-free flow valve, it must be able to maintain its closed condition against the maximum static head which would exist at the valve inlet when a full bag of formula is suspended above the valve without the pump cassette engaged with the tubing between the valve and the bag and without a shut-off clamp being properly engaged with the tubing between the valve and the bag. When the pump cassette is subsequently installed and engaged with the tubing to pump the fluid at a desired flow rate, the pump in the pump cassette must overcome the resiliency of the closed valve to open the valve so that the flow metered by the pump cassette is forced through the valve and into the patient.
It would be desirable for the valve to open at a pressure that is not too much greater than the static head pressure at the inlet of the valve so that the pumping power requirement can be minimized. If the pump is accidentally dislodged or purposely removed without installing an intervening clamp to shut off the tubing between the bag and the patient, then the open valve must close against the static head to prevent free-flow from the bag under the influence of gravity. Thus, the open valve must have sufficient resiliency to close against the static head.
For a given downstream pressure, a conventional flexible, self-sealing valve typically opens at a predetermined minimum upstream inlet pressure (“opening pressure”), but when open, closes only when the upstream inlet pressure is reduced to some value that is significantly less than the predetermined minimum upstream opening pressure. This difference between the upstream pressures at which the valve opens and closes must be taken into account to insure that (1) the pump cassette will be able to open the valve, and (2) the valve will be able to re-close if the pump cassette is removed and the open valve is subjected to the static head from the bag.
In order to minimize the energy requirement of the pump in the pump cassette, the inventor has discovered that it would be desirable to provide an improved flexible, self-sealing valve in which the valve closes when the pressure is close to (but still below) the minimum pressure at which the valve initially opens—it being understood that the maximum upstream pressure at which the valve is able to close (i.e., self-seal) is slightly less than the minimum upstream pressure at which the valve opens, and both the maximum closing pressure and the minimum opening pressure are each greater than the maximum static head pressure that would exist at the valve inlet if the pump cassette were disengaged from the tubing.
The inventor of the present invention has discovered that such an improved valve that opens and closes at pressures that are relatively close can be advantageously used in various applications, including, but not limited to, enteral feeding pumps, intravenous pumps, infusion sets, and other pump sets.
The inventor of the present invention has also determined that it would be particularly desirable to provide a valve having a relatively “crisp” opening and closing action (i.e., a quick and sure opening and closing operation) so as to minimize or limit fluid dripping or minor leakage.